Radio circuit for channel reception



July 12, 1938.

R. H. WQRRALL RADIO CIRCUIT FOR CHANNEL RECEPTION Filed May 11, 1936 T0LE STAGES 2 ND. BET. fi/VD AUDIO INVENTOR Robert" H. WorraZZ ATTORNEYPatented July 12, 1938 UNITED STATES orrirs 29 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) My invention relates broadly toradio receiving circuits and, more particularly, to those suitable forchannel type reception.

One object of my invention is to provide a means for amplification andfor continuous reception at substantially constant audio frequency oftransmitted electrical oscillations whose frequency may vary over apredetermined range.

Another object of my invention is to provide a means for secretcommunication whereby transmitted electrical oscillations, variedpurposely over a predetermined frequency range, at any desired timeintervals, may be received continuously, without appreciable change inthe frequency of the audio signal.

Other and further objects of my invention will be apparent from thefollowing specification, by reference to the accompanying drawing, inwhich two circuits embodying the principles of my invention, arediagrammatically illustrated.

The circuits herein described were developed with a view toward enablingan operator, receiving transmitted radio signals of a relativelyconstant frequency, to continue undiminished reception unhampered bydrifting of the transmitted frequency from its assigned value. Toaccomplish this, in the present invention, I use two similar, parallelinput circuits, each containing an input thermionic tube with necessaryconnections, an oscillator, so arranged that its output will beat withthe output of said tube, a detector stage that operates on the beatfrequencies thus produced, and a filter unit. The outputs of the filterunits are combined in a mixing circuit, from which the resultant energyis led through intermediate frequency amplifiers, a second detector, andaudio frequency stages of a conventional superheterodyne receivingcircuit. In the preferred embodiment of my invention, the oscillators inthe said two input circuits are so tuned that the difference betweentheir output frequencies is always equal to the frequency for which theintermediate stages of the superheterodyne receiving circuit are tuned.Then, by the means a and methods described herein, the received audiosignal will remain substantially unchanged in frequency while thefrequency of the transmitted signal may drift over a range equal to thesaid frequency for which the intermediate superheterodyne stages aretuned; and the said audio signal will remain likewise substantiallyunchanged in volume, so long as the amplitude of the transmittedoscillations remains effectively constant.

Referring to the circuit illustrated in the accompanying drawing, 1 isan antenna or other suitable collector of radiant energy. From thiscollector, two independent branches take off, one of which leads throughcoupling coil 2 to ground, and the other, through coupling coil 3,likewise to ground. Inductive coupling coils are shown in the drawingfor the purpose of illustration, but any convenient type of couplingmeans may be used.

One branch circuit continues from coupling means 2 which serves to feedthe input of thermionic tube ll, which may be of any type suitable foruse in a tuned or untuned input circuit. The output circuit of tube tincludes one of the primary windings of a two primary oscillationtransformer 6, the other primary of which is included in the outputcircuit of an independent self-oscillating circuit 8. The output fromthe secondary of the transformer t feeds the input of thermionicdetector tube Hl, which may be of any type suitable for use as adetector. The output from detector tube ii] is led through a wave filterl2, and thence to one primary of a mixing transformer it, which is of aconventional type, having two primaries and one secondary.

Returning to coupling means 3, a second branch circuit, similar to theone just described, is associated therewith and proceeds by identicalsteps through input tube 5, similar to 4; oscillation transformer l,similar to t, where the output from oscillator 9, similar to 8, ties in;detector tube H, similar to ill; wave filter i3, similar to IE; and theother primary of mixing transformer i l, wherein it joins the branchcircuit associated with coupling means 2.

As to the combined circuit beyond the secondary of mixing transformerHi, this transformer has a tuning condenser it connected across it. Inthe preferred embodiment of my invention, the output of transformer itand condenser l5 may be fed directly to the input of thermionic tube l6.Referring to the drawing, the circuit here described is illustrated whenthe portion embraced between the two broken lines is omitted. The tubeit, which may be of any convenient type suitable for the purpose, isused as a mixing tube, and its output proceeds to feed the intermediatefrequency, second detector, and audio fequency stages of a conventionalsuperheterodyne receiver, as indicated in the drawing.

In a modification of my invention, which is illustrated in the drawingby including in the circuit the portion embraced between the brokenlines, the output from the secondary of mixing transformer It, havingtuning condenser 15 connected across it as before, is fed to the inputof thermionic tube H, which may have characteristics similar to those oftubes 1 and 5. The output of this tube then joins the output of anotherindependent, self-oscillating circuit 118 as these two outputs are eachled through one primary winding of the double primary oscillationtransformer I 9, which is of a conventional type, similar to 6 and l.The output from. the secondary of this transformer, having tuningcondenser 29,

similar to l5, connected across it, is then fed to the input of tube 16,whose output proceeds on to the superheterodyne circuit in exactly thesame manner as previously described for the preferred embodiment.

Plate power is supplied to the entire circuit by connecting the positiveterminal of a source of potential to the junction points of the doubleprimaries in the transformers 6, l, M, and i9, when the portion of thecircuit associated therewith is used. These points are indicated in thedrawing by +B. The negative terminal of the plate power source isgrounded. The circuit is grounded at the ends of coupling means 2 and 3,and, through blocking condensers, at the plates of the tubes inoscillators 8, 9, and 18. These points are indicated in the drawing bythe conventional symbol. Filament power and biasing potential may besupplied by usual means.

In using the principles of this invention in practice, the tubes of theoscillator 8 and the detector l0 may be combined by using a pentagridconvertor, with associated circuits. This also applies to the tubes ofoscillator 9 and detector H, and those of oscillator i8 and mixer It.Any of the oscillators described or shown may be crystal orelectro-mechanically controlled.

To explain the operation of the circuit, let us assume that theintermediate frequency stages of the superheterodyne circuit be turnedfor 400 kcs., and that the frequency being received is 10,005 kcs. Underthese conditions, the oscillator 8 is set to produce a frequency of10,200 kcs., and oscillator 9 to an output frequency of 9,800 kcs. Thedifference between these latter two frequencies, when using thepreferred embodiment of my invention, must always be equal to theintermediate channel frequency, and it is convenient to have thisdifference approximately equally spaced on either side of the incomingfrequency. Following a signal through the circuit, and looking first atthe circuits associated with tubes 4 and E0, the incoming frequency of10,005 kcs. passes through the input tube 4, and beats, in theoscillation transformer 6 with the frequency of 10,200 kcs. from theoscillator 8. This produces in the plate circuit of detector tube [0,the sum and difference frequencies of 20,205 and kcs., plus theoscillator frequency of 10,200 kcs. These frequencies are all passed tothe filter 12, where all are eliminated except 195 kcs., which is passedon to the mixing transformer l4. Looking now at the circuits associatedwith tubes 5 and H, by the same process described above, the sum anddifference frequencies 19,805 and 205 kcs., plus the oscillatorfrequency of 9,800 kcs. from oscillator 9, are all present in the platecircuit of detector tube ll. These frequencies are all passed to thefilter l3, where all are eliminated except 205 kcs., which is passed onto the mixing transformer M. We now have in the primary of the mixingtransformer the two frequencies of 195 and 205 kcs. These two, beatingtogether, produce sum and difference frequencies of 400 to 10 kcs. Inthe preferred form of the circuit, these two frequencies are passed ondirectly to the mixer tube l6. From the mixer tube, both pass on the I.F. stages, where the 400 kcs. is amplified and passed to the seconddetector and audio stages in the customary manner, while the 10 kcs. iseliminated.

From the above analysis, it will be apparent that the transmitterfrequency may drift anywhere between the limits of 9,800 and 10,200kcs.; yet the output of the mixer tube IE will still supply energy at aconstant 400 kcs. to the I. F. stages, and the received audio signalwill remain substantially constant at its original frequency value. Thiswide a permissible variation is extreme, even at 10,000 kcs. By using anintermediate frequency, of say 25 kcs., the allowable drift in thetransmitted frequency may be narrowed down to plus or minus 12.5 kcs.

If it is desired still further to control the intermediate channel, themodification of my invention, employing the circuits associated with theinput tube ll, may be used. Looking back to the output of the mixingtransformer M, in the example we have taken, frequencies of 400 and 10kcs. are impressed upon tube IT, and are present in its output. Anotherfrequency from independent oscillator i8 is brought in to beat withthese two frequencies in oscillation transformer l9. By properlycontrolling the value of the frequency from the oscillator l8, beatfrequencies of any desired value may be produced, thus permitting theuse of any convenient intermediate frequency channel for theintermediate frequency stages of the superheterodyne circuit.

It will now be apparent from the foregoing discussion that as long asany component of the incoming signal of the frequency chosen for thetuned intermediate frequency superheterodyne stages, is impressed uponthe input of the mixer tube i6, whether directly from the output ofmixing transformer M or from the output of oscillation transformer 99,the circuit will function as previously described, regardless of thesimultaneous impression upon the input of said mixer tube E0 of elementsof other frequencies desirable to increase the width of the frequencyband over which the apparatus will operate, or to perform the designedfunction by means of a number of stages bracketing limited frequencybands, the received oscillations may be divided into multiple componentsin the same manner as described in connection with coupling means 2 and3, and these components may each be operated upon through circuitssimilar to those from 2 and 3 to M, then joined with other components inone or a series of mixing devices, while the general principles ofoperation hereinbefore disclosed will remain the same.

Should it be desirable at any time to shift to other receiving channels,the tuning condensers of oscillators 8 and 9 may be set to new values,and the rest of the circuit will function automatically over the newlychosen band.

The invention disclosed herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

I claim:

1. A method of amplifying a received radio frequency current of unstablefrequency which comprises dividing it into two substantially equalparts, beating one of said parts with a first substantially constantfrequency to produce a first beat frequency corresponding to thedifference in frequency between the received current and said firstsubstantially constant frequency, simultaneously beating the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency by apredeterminedamount, to produce a second beat frequency corresponding tothe difference in frequency between the received. current and saidsecond substantially constant frequency, combining these said first andsecond beat frequencies to produce a signal current having a frequencycorresponding to the difference between the said first and secondsubstantially constant frequencies and equal to the sum of the saidfirst and second beat frequencies, then amplifying and detaching thislast said signal current.

2; A method of deriving a signal current of substantially constantfrequency from a received radio frequency current of unstable frequencywhich comprises dividing the received current into two substantiallyequal parts, beating one of said parts with a first substantiallyconstant frequency to produce a first beat frequency corresponding tothe difference in frequency between the received current and said firstsubstantially constant frequency, simultaneously beating the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency bya predeterminedamount, to produce a second beat frequency corresponding to thedifference in frequency between the received current and said secondsubstantially constant frequency, then combining these said first andsecond beat frequencies to produce a signal current having a frequencycorresponding to the difference between the said first and secondsubstantially constant frequencies and equal to the sum of the saidfirst and second beat frequencies.

3. A method of amplifying a received radio frequency'current of unstablefrequency which comprises dividing it into two substantially equalparts, beating one of said parts with a first substantially constantfrequency to produce a first beat frequency corresponding to thedifference in frequency between the received current and said firstsubstantially constant frequency, simultaneously beating the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency by a predeterminedamount, to produce a second beat frequency corresponding to thedifference in frequency between the received current and said secondsubstantially constant frequency, combining these said first and secondbeat frequencies to produce a signal current having a frequencycorresponding to the difference between the said firstand secondsubstantially constant frequencies and equal to the sumof the said firstand second beat frequencies, beating this said signal current with athird substantially constant frequency which may be adjusted to produceanother signal current of any desired frequency, then amplifying anddetecting this last said signal current.

4. A method of deriving a signal current of any desiredsubstantiallyconstant frequency from a received radio frequency currentof unstable frequency which comprises dividing it into two substantiallyequal parts, beating one of said parts with a first substantiallyconstant frequency to producea first beat frequency corresponding to thedifference in frequency between the received current and said firstsubstantially constant frequency, simultaneously beating the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency by a predeterminedamount, to produce asecond beat frequency corresponding to thedifference in frequency between the received current and saidsecondsubstantially constant frequency, combining these said first and secondbeat frequencies to produce a signal current having a frequencycorresponding to the difference between the said first and secondsubstantially constant frequencies and equal to the sum of the saidfirst and second beat frequencies, then beating this said signal currentwith a third substantially constant frequency which may be adjusted toproduce a final signal current of any desired frequency.

5. A method of amplifying any received radio frequency currents within apredetermined frequency band which comprises dividing all of suchreceived currents into two substantially equal parts, beating all of thefrequencies in one of said parts with a first substantially constantfrequency to produce a first group-of beat frequencies, selecting fromthese the beat frequencies corresponding to the differences in frequencybetween the received currents and said first substantially constantfrequency, simultaneously beating all of the frequencies in the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency'by the width of thesaid predetermined frequency band, to produce a second group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between the received currents and saidsecond substantially constant frequency, combining all of the previouslyselected beat frequencies to produce a third group of beatfrequencies,selecting from said third group of beat frequencies allthose having a frequency similar to the difference between the saidfirst and second substantially constant frequencies and likewise to thewidth of the said predetermined frequency band, combining these lastselected similar frequencies to produce a signal current, thenamplifying and detecting this last said signal current. I

6. A method of deriving a signal current of substantially constantfrequency from any received radio frequency currents within apredetermined frequency band which comprises dividing all of suchreceiving currents into two substantially equal parts, beating all ofthe frequencies in one of said parts with a first substantially constantfrequency to produce a first group of beat frequencies, selecting fromthese the beat frequencies corresponding to the differences in frequencybetween the received currents and said first substantially constantfrequency, simultaneously beating all of the frequencies in the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency by the width of'the said'p-redetermined frequency band, to produce a second group ofbeat frequencies, selecting from these the beat frequenciescorresponding to the differences in frequency between the receivedcurrents and said second substantially constant frequency, combining allof the previously selectedbeatfrequencies to produce a third group ofbeat frequencies selecting from said third group of beat frequencies allthose having a frequency similar to the difference between the saidfirst and second substantially constant frequencies and likewise to thewidth of the said predetermined frequency band, then combining theselast selected similar frequencies to produce a resultant signal current.

'7. A method of amplifying any received radio frequency currents withina predetermined frequency band'which comprises dividing all of suchreceived currents into two substantially equal parts, beating all of thefrequencies in one of said parts with a first substantially constantfrequency to produce a first group of beat frequencies, selecting fromthese the beat frequencies corresponding to the differences in frequencybetween the received currents and said first substantially constantfrequency, simultaneously beating all of the frequencies in the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency by the width of thesaid predetermined frequency band, to produce a second group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between the received currents and saidsecond substantially constant frequency, combining all of the previouslyselected beat frequencies to produce a third group of beat frequencies,selecting from said third group of beat frequencies all those having afrequency similar to the difference between the said first and secondsubstantially constant frequencies and likewise to the Width of the saidpredetermined frequency band, combining these last selected similarfrequencies to produce a signal current, beating this said signalcurrent with a third substantially constant frequency which maybe'adjusted to produce another signal current of any desired frequency,then amplifying and detecting this last said signal current.

8. A method of deriving a signal current of any desired substantiallyconstant frequency from any received radio frequency currents within apredetermined frequency band which comprises dividing all of suchreceived currents into two substantially equal parts, beating all of thefrequencies in one of said parts with a first substantially constantfrequency to produce a first group of beat frequencies, selecting fromthese the beat frequencies corresponding to the differences in frequencybetween the received currents and said first substantially constantfrequency, simultaneously beating all of the frequencies in the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency by the width of thesaid predetermined frequency band, to produce a second group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between the received currents and saidsecond substantially constant frequency, combining all of the previouslyselected beat frequencies to produce a third group of beat frequencies,selecting from said third group of beat frequencies all those having afrequency similar to the difference between the said first and secondsubstantially constant frequencies and likewise to the width of the saidpredetermined frequency band, combining these last selected similarfrequencies to produce a signal current, then beating this said signalcurrent with a third substantially constant frequency which may beadjusted to produce a resultant signal current of any desired frequency.

9. A method of amplifying any received radio frequency currents within apredetermined frequency band which comprises dividing all of suchreceived currents into two substantially equal parts, beating all of thefrequencies in one of said parts with a first substantially constantfrequency to produce a first group of beat frequencies, selecting fromthese the beat frequencies corresponding to the differences in frequencybetween the received currents and said first substantially constantfrequency, simultaneously beating all of the frequencies in the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constantfrequency by the width of thesaid predetermined frequency band, to produce a second group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between the received currents and saidsecond substantially constant frequency, combining all of the previouslyselected beat frequencies to produce a third group of beat frequencies,beating said third group of beat frequencies with a third substantiallyconstant frequency which may be adjusted to produce a signal current ofany desired frequency, then amplifying and detecting this last saidsignal current.

10. A method of deriving a signal current of any desired substantiallyconstant frequency from any received radio frequency currents within apredetermined frequency band which ,comprises dividing all of suchreceived currents into two substantially equal parts, beating all of thefrequencies in one of said parts with a first substantially constantfrequency to produce a first group of beat frequencies, selecting fromthese the beat frequencies corresponding to the differences in frequencybetween the received currents and said first substantially constantfrequency, simultaneously beating all of the frequencies in the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency by the width of thesaid predetermined frequency band, to produce a second group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between the received currents and saidsecond substantially constant frequency, combining all of the previouslyselected beat frequencies to produce a third group of beat frequencies,then beating said third group of beat frequencies with a thirdsubstantially constant frequency which may be adjusted to produce aresultant signal current of any desired frequency.

11. A method of amplifying any received modulated carrier signalcurrents within a predetermined frequency band which comprises dividingall of such received currents into two substantially equal parts,beating all of the frequencies in one of said parts with a firstsubstantially constant frequency to produce a first group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between the received currents and saidfirst substantially constant frequency, simultaneously beating all ofthe frequencies in the other of said parts with a second substantiallyconstant frequency, differing from the said first substantially constantfrequency by the width of the said predetermined frequency band, toproduce a second group of beat frequencies, selecting from these thebeat frequencies corresponding to the differences in frequency betweenthe received currents and said second substantially constant frequency,combining all of the previously selected beat frequencies to produce athird group of beat frequencies, selecting from said third group of beatfrequencies all those having a frequency similar to the differencebetween the said first and second substantially constantfrequencies andlikewise to the width of the said predetermined frequency band,combining these last selected similar frequencies to produce a modulatedsignal current, then amplifying and detecting this last said modulatedsignal current.

12. A method of deriving a signal modulated current of substantiallyconstant fundamental frequency but of variable amplitude from anyreceived modulated carrier signal currents within a predeterminedfrequency band which comprises dividing all of such received currentsinto two substantially equal parts, beating all of the frequencies inone of said parts with a first substantially constant frequency toproduce a first group of beat frequencies, selecting from these the beatfrequencies corresponding to the differences in frequency between thereceived currents and said first substantially constant frequency,simultaneously beating all of the frequencies in theother of said partswith a second substantially constant frequency, differing from thesaidfirst substantially constant frequency by the width of the saidpredetermined frequency band, to produce asecond group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between the received currents and saidsecond substantially constant frequency, combining all of the previouslyselected beat frequencies to produce a third group of beat frequencies,selecting from said third group of beat frequencies all those having afrequency similar to the difference between the said first and secondsubstantially constant frequencies and likewise to the width of the saidpredetermined frequency band, then combining these last selected similarfrequencies to produce a resultant signal modulated current.

13. A method of amplifying any received modulated carrier signalcurrents within a predetermined frequency band which comprises dividingall of such received currents into two substantially equal parts,beating all of the frequencies in one of said parts with a firstsubstantially constant frequency to produce a first group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between'the received currents and saidfirst substantially constant frequency, simultaneously beating all ofthe frequencies in the other of said parts with a second substantiallyconstant frequency, differing from the said first substantially constantfrequency by the width of the said predetermined frequency band, toproduce a second group of beat frequencies, selecting from these thebeat frequencies corresponding to the differences in frequency betweenthe received currents and said second substantially constant frequency,combining all of the previously selected beat frequencies to produce athird group of beat frequencies, beating this said third group of beatfrequencies with a third substantially constant frequency which may beadjusted to produce a modulated signal current of any desiredfundamental frequency, then amplifying and detecting this last saidmodulated signal current.

14. A method of deriving a signal modulated current of any desiredsubstantially constant fundamental frequency but of variable amplitudefrom any received modulated carrier signal currents within apredetermined frequency band which comprises dividing all of suchreceived currents into two substantially equal parts, beatingall of thefrequencies in one of said parts with a'first substantially constantfrequency to produce a first group of beat frequencies, selecting fromthese the beat frequencies corresponding to the differences in frequencybetween the received currents and said first substantially constantfrequency, simultaneously beating all of the frequencies in the other ofsaid parts with a second substantially constant frequency, differingfrom the said first substantially constant frequency by the width of thesaid predetermined frequency band, to produce a second group of beatfrequencies, selecting from these the beat frequencies corresponding tothe differences in frequency between the received currents and saidsecond substantially constant frequency, combining all of the previouslyselected beat frequencies to produce a third group of beat frequencies,then beating this said third group of beat frequencies with a thirdsubstantially constant frequency which may be adjusted to produce asignal modulated current of any desired substantially constantfrequency.

15. A method of amplifying any radio frequency currents within apredetermined frequency band which comprises separately beating each oftwo or more similar components of received currents with a differentsubstantially constant frequency, the largest difference between whichsaid substantially constant frequencies de termines the Width of saidpredetermined frequency band, selecting and combining the beatfrequencies thus produced to supply a signal current whose frequencycorresponds to the difference between two of said substantially constantfrequencies, then amplifying and detecting said signal current.

16. A method of deriving .a signal current of substantially constantfrequency from any radio quency band which comprises separately beating.

each of two or more similar components of received currents with adifferent substantially constant frequency, the largest differencebetween which said substantially constant frequencies determines thewidth of said predetermined frequency band, selecting and combining thebeat frequencies thus produced to supply a signal current whosefrequency corresponds to the difference between two of saidsubstantially constant frequencies, beating this said signal currentwith a substantially constant frequency which may be adjusted to produceanother signal current of 1 any desired frequency, then amplifying anddetecting this last said signal current.

18. A method of deriving a signal current of any desired substantiallyconstant frequency from any radio frequency currents within apredetermined frequency band which comprises separately beating each oftwo or more similar components of received currents with a differentsubstantially constant frequency, the largest difference between whichsaid substantially constant frequencies determines the width of saidpredetermined frequency band, selecting .and combining the beatfrequencies thus produced to supply a signal current whose frequencycorresponds to the difference between two of said substantially constantfrequencies, then beating this said signal current with a substantiallyconstant frequency which may be adjusted to produce another signalcurrent of any desired frequency.

19. A method of amplifying any modulated carrier signal currents withina predetermined frequency band which comprises separately beating eachof two or more similar components of received currents with a differentsubstantially constant frequency, the largest difference between whichsaid substantially constant frequen cies determines the width of saidpredetermined frequency band, selecting and combining the beatfrequencies thus produced to supply a modulated signal current whosefrequency corresponds to the difference between two of saidsubstantially constant frequencies, then amplifying and detecting saidmodulated signal current.

20. A method of deriving a signal modulated current of substantiallyconstant fundamental frequency but of variable amplitude from anymodulated carrier signal currents within a predetermined frequency bandwhich comprises separately beating each of two or more similarcomponents of received currents with a different substantially constantfrequency, the largest difference between which said substantiallyconstant frequencies determines the width of said predeterminedfrequency band, selecting and combining the beat frequencies thusproduced to supply a signal modulated current whose frequencycorresponds to the difference between two of said substantially constantfrequencies.

21. A method of amplifying any modulated carrier signal currents withina predetermined frequency band which comprises separately beating eachof two or more similar components 'of received currents with a differentsubstantially constant frequency, the largest difference between whichsaid substantially constant frequencies determines the width of saidpredetermined frequency band, selecting and combining the beatfrequencies thus produced to supply a modulated signal current whosefrequency corresponds to the difference between two of saidsubstantially constant frequencies, beating this said modulated signalcurrent with a substantially constant frequency which may be adjusted toproduce another modulated signal current of any desired fundamentalfrequency, then amplifying and detecting this last said modulated signalcurrent.

22. A method of deriving a signal modulated current of any desiredsubstantially constant fundamental frequency but of variable amplitudefrom any modulated carrier signal currents within a predeterminedfrequency band which comprises separately beating each of two or moresimilar components of received currents with a different substantiallyconstant frequency, the largest difference between which saidsubstantially constant frequencies determines the Width of saidpredetermined frequency band, selecting and combining the beatfrequencies thus produced to supply a signal current whose frequencycorresponds to the difference between two of said substantially constantfrequencies, then amplifying and detecting said signal current, thenbeating this said signal modulated current with a substantially constantfrequency which may be adjusted to produce a signal modulated current ofany desired substantially constant frequency.

23. A method of secret communication by radio which comprises purposelyvarying'th'e principal or carrier frequency of transmitted electricaloscillations, within certain predetermined limits, receiving saidoscillations in a collector of radiated energy, dividing saidoscillations into components, separately beating each of said componentswith a different substantially constant frequency, the largestdifference between which said substantially constant frequenciesdetermines the limits within which the said transmitted oscillations maybe varied, selecting and combining the beat frequencies thus produced tosupply a signal current whose frequency corresponds to the differencebetween two of the said substantially constant frequencies, furtheroperating upon this said signal current by additional beating with othersubstantially constant frequencies, detection, and amplification toproduce a final signal current whose principal, or carrier, frequencywill remain substantially constant, independent of the frequencyvariation of the said transmitted oscillations within the predeterminedlimits, and converting this said final signal current in a signalresponsive device, whereby continuous reception, which would otherwisebe interrupted, may be accomplished on transmitted oscillations ofvarying frequency.

24. A method of secret communication by radio which comprises purposelyvarying the principal or carrier frequency of transmitted electricaloscillations, within certain predetermined limits, receiving saidoscillations in a collector of radiated energy, dividing saidoscillations into components, separately beating each of said componentswith a different substantially constant frequency, the largestdifference between which said substantially constant frequenciesdetermines the limits within which the said transmitted oscillations maybe varied, selecting and combining the beat frequencies thus produced tosupply a signal current whose frequency corresponds to the differencebetween two of the said substantially constant frequencies, furtheroperating upon this said signal current by detection and amplificationto produce a final signal current whose principal, or carrier, frequencywill remain substantially constant, independent of the frequencyvariation of the said transmitted oscillations within the predeterminedlimits, and converting this said final signal current in a signalresponsive device, whereby continuous reception, which would otherwisebe interrupted, may be accomplished on transmitted oscillations ofvarying frequency.

25. In a radio signal receiving station; means for intercepting incomingradio frequency waves; means for producing from such a wave a pluralityof substantially identical components; a plurality of substantiallyidentical circuits, each actuated by a different one of said componentsand each including, means for coupling electrically to said componentproducing means, a thermionic input tube connected in circuit with saidcoupling means so that the grid circuit of said tube will be controlledby said actuating component, heterodyning means adjustable to produce anindividual substantially constant frequency, means for producinginteraction between said heterodyning means and the radio frequencycurrents caused to flow in the output circuit of said input tube as aresult of said actuating component acting upon said grid circuit,detecting means operating upon the beat frequency currents produced bysaid interaction, and filtering means operating upon the detectedcurrents in the outputof said detecting means to pass only currentswithin a selected frequency band; means for combining the selectedfrequency currents from all of said substantially identical circuits toproduce signal currents having a substantially constant frequency equalto the difference between said individual frequencies of two of saidheterodyning means; an output circuit, actuable by said signal currents,and including signal responsive means; and means for coupling saidoutput circuit to said combining means.

26. In a radio signal receiving station; means for intercepting incomingradio frequency waves; means for producing from such a wave a pluralityof substantially identical components; a plurality of substantiallyidentical circuits, each actuated by a different one of said componentsand each including, means for coupling electrically to said componentproducing means, a thermionic input tube connected in circuit with saidcoup-ling means so that the grid circuit of said tube will be controlledby said actuating component, heterodyning means adjustable to produce anindividual substantially constant frequency, means for producinginteraction between said heterodyning means and the radio frequencycurrents caused to flow in the output circuit of said input tube as aresult of said actuating component acting upon said grid circuit,detecting means operating upon the beat frequency currents produced bysaid interaction, and filtering means operating upon, the detectedcurrents in the output of said detecting means to pass only currentswithin a selected frequency band; means for combining the selectedfrequency currents from all of said substantially identical circuits toproduce signal currents having a substantially constant frequency equalto the difference between said individual frequencies of two of saidheterodyning means; an intermediate circuit comprising an inputthermionic tube and additional heterodyning means; means for couplingsaid intermediate circuit to said combining means; an output circuit,actuable by said signal currents, and including signal responsive means;and means for coupling said output circuit to the output of saidintermediate circuit.

27. In a radio signal receiving station; means for intercepting incomingradio frequency waves; means for producing from such a wave twosubstantially identical components; two substantially identicalcircuits, each actuated by a different one of said components and eachincluding, means for coupling electrically to said component producingmeans, a thermionic input tube connected in circuit with said couplingmeans so that the grid circuit of said tube will be controlled by saidactuating component, heterodyning means ad-' justable to produce anindividual substantially constant frequency, means for producinginteraction between said heterodyning means and the radio frequencycurrents caused to flow in the output circuit of said input tube as aresult of said actuating component acting upon said grid circuit,detecting means operating upon the beat frequency currents produced bysaid interaction, and filtering means operating upon the detectedcurrents in the output of said detecting means to pass only currentswithin a selected frequency band; means for combining the selectedfrequency currents from both of said substantially identical circuits toproduce signal currents having a substantially constant frequency equalto the difference between the individual frequencies of saidheterodyning means; an output circuit, actuable by said signal currents,and including signal responsive means; and means for coupling saidoutput circuit to said combining means.

28. In a radio signal receiving station; means for intercepting incomingradio frequency waves; means for producing from such a wave twosubstantially identical components; two substantially identicalcircuits, each actuated by a different one of said components and eachincluding, means for coupling electrically to said component producingmeans, a thermionic input tube connected in circuit with said couplingmeans so that the grid circuit of said tube will be controlled by saidactuating component, heterodyning means adjustable to produce anindividual substantially constant frequency, means for producinginteraction between said heterodyning means and the radio frequencycurrents caused to fiow in the output circuit of said input tube as aresult of said actuating component acting upon said grid circuit,detecting means operating upon the beat frequency currents produced bysaid interaction, and filtering means operating upon the detectedcurrents in the output of said detecting means to pass only currentswithin a selected frequency band; means for combining the selectedfrequency currents from both of said substantially identical circuits toproduce signal currents having a substantially constant frequency equalto the difference between the individual frequencies of saidheterodyning means; an intermediate circuit comprising an inputthermionic tube and additional heterodyning means; means for couplingsaid intermediate circuit to said combining means; an output circuit,actuable by said signal currents, and including signal responsive means;and means for coupling said output circuit to the output of saidintermediate circuit.

29. In a radio signal receiving station; means for intercepting incomingradio frequency waves; means for producing from such a wave a pluralityof substantially identical components; a plurality of substantiallyidentical circuits, each actuated by a different one of said componentsand each including, means for coupling electrically to said componentproducing means, a thermionic input tube connected in circuit with saidcoupling means so that the grid circuit of said tube will be controlledby said actuating component, heterodyning means adjustable to produce anindividual substantially constant frequency, means for producinginteraction between said heterodyning means and the radio frequencycurrents caused to flow in the output circuit of said input tube as aresult of said actuating component acting upon said grid circuit,detecting and filtering means operating upon the beat frequency currentsproduced by said interaction to produce detected currents within aselected fraquency band; means for combining the detected currents fromsaid substantially identical circuits to produce signal currents havinga substantially constant frequency equal to the difference between thefrequencies of two of said heterodyning means; an output circuit,actuable by said signal currents, including intermediate amplifyingstages and signal responsive means; and means for coupling said outputcircuit to said combining means.

ROBERT H. WORRALL.

